A quantitative synthesis of the role of birds in carrying ticks and tick-borne pathogens in North America

Abstract

Birds play a central role in the ecology of tick-borne pathogens. They expand tick populations and pathogens across vast distances and serve as reservoirs that maintain and amplify transmission locally. Research into the role of birds for supporting ticks and tick-borne pathogens has largely been descriptive and focused in small areas. To expand inference beyond these studies, we conducted a quantitative review at the scale of North America to identify avian life history correlates of tick infestation and pathogen prevalence, calculate species-level indices of importance for carrying ticks, and identify research gaps limiting understanding of tick-borne pathogen transmission. Across studies, 78 of 162 bird species harbored ticks, yielding an infestation prevalence of 1981 of 38,929 birds (5.1 %). Avian foraging and migratory strategies interacted to influence infestation. Ground-foraging species, especially non-migratory ground foragers, were disproportionately likely to have high prevalence and intensity of tick infestation. Studies largely focused on Borrelia burgdorferi, the agent of Lyme disease, and non-migratory ground foragers were especially likely to carry B. burgdorferi-infected ticks, a finding that highlights the potential importance of resident birds in local pathogen transmission. Based on infestation indices, all "super-carrier" bird species were passerines. Vast interior areas of North America, many bird and tick species, and most tick-borne pathogens, remain understudied, and research is needed to address these gaps. More studies are needed that quantify tick host preferences, host competence, and spatiotemporal variation in pathogen prevalence and vector and host abundance. This information is crucial for predicting pathogen transmission dynamics under future global change.

Repeatable differences in exploratory behaviour predict tick infestation probability in wild great tits

“…exploratory behaviour and body condition) might explain tick burden of infested birds. This could be other behaviours such as aggression (Zohdy et al 2017) or foraging behaviour (Newman et al 2015; Loss et al 2016; Kocianová et al 2017) as both play roles in tick burden.…”

“…Tick burden can also vary among individual birds as a function of individual-specific traits, such as behaviour (Barber and Dingemanse 2010; Newman et al 2015; Sih et al 2018) or body condition (Norte et al 2013; Newman et al 2015). For instance, bird species with larger average body sizes have increased tick burdens compared to smaller bird species (Newman et al 2015) as do bird species with a higher proportion of ground foraging behaviour (Newman et al 2015; Loss et al 2016; Kocianová et al 2017). Similarly, within populations of the same species, individual-specific differences in foraging or social behaviour can also predict tick burdens (Sih et al 2018).…”

Life history characteristics of birds influence patterns of tick parasitism

“…Ticks serve as hosts for a large number of zoonotic pathogens and the relative importance of birds in supporting tick life cycles and as reservoirs for vector-borne pathogens has gained attention of recent years [1][2][3]. Bird migration and dispersal have been implicated in the spread of tick-transmitted pathogens in Europe and North America [4][5][6][7][8] and potentially serve as a common mechanism for range expansion of vector-borne pathogens [2].…”

“…Bird migration and dispersal have been implicated in the spread of tick-transmitted pathogens in Europe and North America [4][5][6][7][8] and potentially serve as a common mechanism for range expansion of vector-borne pathogens [2]. Migratory movement of bird-associated Ixodes scapularis ticks infected with the Lyme disease agent, Borrelia burgdorferi, may explain recently observed northward and southward geographic expansion of human Lyme disease cases [1,3,5,[8][9][10][11][12]13] and a theoretical mathematical analysis demonstrated that deposition of ticks by migrating birds can enhance tick population growth and thus increase human risk of tick-borne disease [14]. Moreover, the recent establishment of the disease vector long-horned tick, Haemaphysalis longicornis, in New Jersey, USA, and its subsequent detection in a number of other states underscores the rapidity with which our understanding of geographic distributions of ticks can change [15].…”

“…Moreover, many of the B. burgdorferi genotypic variants detected in birds have been previously unreported, suggesting that bird-tick transmission cycles may contribute to the maintenance of genetic variation in this pathogenic bacterium [9,19,21]. Although certain small mammal species are likely to be most important in terms of enzootic transmission and maintenance of this pathogen [22], birds may play an important role in the evolutionary ecology and long-distance movement of B. burgdorferi [3].…”